6.7L Power Stroke Engine and DrivetrainDiscussion of the 6.7L Power Stroke diesel engine and drivetrain in the 2011-Up Super Duty trucks. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 6.7L Power Stroke engine.

I put some new tires on my truck that are only 1 inch taller and about 3/4 inch wider (original 265/70/17) and new tires 285/70/17. Running at 80 psi. I did not think there would be very much difference at all. I lost 5.5 mpg on my drive to Houston on cruise control at 65 mph. Also been losing mpg steadily since the first time I hand-calculated at 21.7 mpg driving 65 on cruise control on the highway steady-state. Last mileage check at right under 11000 miles showed 18.5 hand-calculated with fuel right at edge of fill port. I hand-calculated 13.5 mpg with the new tires. Will take it in to a ford dealer up here to get them to adjust tire size in computer. If that doesn't stop the slide in mileage I am getting rid of this truck. With diesel prices ramping up and no end in sight, I cannot be driving this vehicle if it keeps getting worse and worse mileage like it has been doing.

Any one have any suggestions or experienced this same problem? Truck is box-stock except for ranch-hand bumper replacement on front and the new [very slightly larger] tires. If I knew this was going to happen, I would have: 1) not bought this truck to start with, and 2) would not have put bigger tires on it.

I am extremely disappointed. I think I may trade this truck off before putting many more miles on it. I definitely DO NOT RECOMMEND ANYONE BUYING ONE OF THESE NEW FORD TRUCKS!!!!!!!! Since first check at 3000 miles, it has lost 8.5 mpg.

Before you do something rash, get the computer reset for the new tire size, not only is your speedo off, so is your ODOMETER, which will throw off your hand calculated mileage. Also, its winter and as such winter blend diesel is being sold at most stations in the US. Winter blend contiains kero. which has less heat capacity per galon than diesel. Therefore it takes more of it to produce the same amount of work as a gal. of diesel. Also in winter when the truck is cold, the computer employs a cold start strategy that will enrich the mixure for easier starting and warm up, this consumes additional fuel. Further the parasitic losses are higher in cold temps, the tranny, rear/front ends and crankcase oils are thick when cold and take more time to warm up to optimal temps, thus causing increased drag. There may be other things but thes will account for most of your mpg dropoff.
I've driven diesels for better than 20 years and during the winter all of them experienced lower mileage, but returned in the summer.
BTW the tire size increase will have an effect on your overall rear gearing, however slight, that will cause you to use slightly more fuel to accelerate from a dead stop.

I put some new tires on my truck that are only 1 inch taller and about 3/4 inch wider (original 265/70/17) and new tires 285/70/17. Running at 80 psi. I did not think there would be very much difference at all. I lost 5.5 mpg on my drive to Houston on cruise control at 65 mph. Also been losing mpg steadily since the first time I hand-calculated at 21.7 mpg driving 65 on cruise control on the highway steady-state. Last mileage check at right under 11000 miles showed 18.5 hand-calculated with fuel right at edge of fill port. I hand-calculated 13.5 mpg with the new tires. Will take it in to a ford dealer up here to get them to adjust tire size in computer. If that doesn't stop the slide in mileage I am getting rid of this truck. With diesel prices ramping up and no end in sight, I cannot be driving this vehicle if it keeps getting worse and worse mileage like it has been doing.

Any one have any suggestions or experienced this same problem? Truck is box-stock except for ranch-hand bumper replacement on front and the new [very slightly larger] tires. If I knew this was going to happen, I would have: 1) not bought this truck to start with, and 2) would not have put bigger tires on it.

I am extremely disappointed. I think I may trade this truck off before putting many more miles on it. I definitely DO NOT RECOMMEND ANYONE BUYING ONE OF THESE NEW FORD TRUCKS!!!!!!!! Since first check at 3000 miles, it has lost 8.5 mpg.

Really? Your disapointed? Did you buy the truck for a daily commuter or a work truck? Daily commuter it will never be economical. You put wider, taller tires on with maybe a softer compound, with winter blend fuel. What do you expect? You don't recomend buying a Ford diesel? What diesel do you recomend? The others are no better with mileage.

If you were going with bigger tires the 3.55 gears might have helped keep the mpg steady, but would have been lower to begin with. I agree with whats already on here that most likely other factors are the culprits. These trucks are so heavy and so much power I don't see how a little bigger more aggressive tire would hurt it that much. Also as stated the first run might have been "new truck luck". Even 13.5 mpg isn't bad for a truck with all its capabilities. In comparison most luxury cars don't get much better mpg using premium gas.

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